Study On The Laser Properties Of Yb Ions In Tetragonal Structure LuPO₄ And LuVO₄ Crystals

Tetragonal orthovanadates of zircon structure have become important host materials for trivalent lanthanide rare-earth active ions;while the isomorphic orthophosphates are also likely to become ideal hosts for these active ions.Among these vanadates and phosphates,LuVO₄ and LuPO₄ are the most suitable for use as host crystals for the Yb ion.It is therefore of practical importance to investigate the laser properties of Yb ion in tetragonal LuVO₄ and LuPO₄ crystals.In this work we conducted an intensive investigation into the spectroscopic properties,pump absorption behavior,continuous-wave laser operation,and passive Q-switching action with Cr⁴⁺:YAG,GaAs,or 2D WS₂ as saturable absorber,of the Yb:LuVO₄ and Yb:LuPO₄ crystals,achieving a series of innovative results.A comparative study of the two crystals shows that for?polarization,the peak absorption or emission cross-section for Yb:LuVO₄ is four times larger than that for Yb:LuPO₄.In respects of laser performance,Yb:LuPO₄ proves to be much superior to Yb:LuVO₄.A maximum output power of 3.30 W was produced with a 0.6 mm thick Yb:LuPO₄ microchip crystal;while the output power attainable with a 2 mm long micro-rod crystal?transverse dimension of⁰.7 mm?could reach 8.35 W.Passively Q-switched laser operation of Yb:LuVO₄ crystal was realized in a simple plano-concave resonator,with Cr⁴⁺:YAG acting as saturable absorber.In pulsed operation induced by a Cr⁴⁺:YAG having an initial transmission of 99.3%,a maximum output power of 2.35 W was produced with a slope efficiency of 25%,the resulting pulse energy and duration were 8.2?J and 39.2 ns.Importantly,the pulse repetition rate,at which the maximum output power was generated,reached 285.7 kHz,nearing its intrinsic upper limit imposed by the recovery time of Cr⁴⁺:YAG..Passive Q-switching laser action of Yb:LuPO₄ micro-rod crystal was achieved in two distinct modes with GaAs saturable absorber,through selection and optimization of laser resonator as well as GaAs crystal parameters and its intracavity position.In the high-repetition-rate high-power?HRHP?mode,5.0 W of output power was generated at333.3 kHz with a slope efficiency of 34%,the shortest pulse duration was 68.1 ns;while in the low-repetition-rate high-energy?LRHE?mode,the highest output power was 0.85W,which was produced at 3.7 kHz,the resulting pulse energy,duration,and peak power were,respectively,230?J,5.5 ns,and 41.8 kW.With the help of a coupled plane-parallel resonator,high-power passively Q-switched laser operation of Yb:LuPO₄ microchip crystal was realized,with 2D WS₂ or WSe₂ serving as saturable absorber,under very high output coupling conditions.The maximum output power,achievable in the case of WS₂ Q-switching,could reach 4.35 W at a repetition rate of 1.33 MHz,with a slope efficiency of 47%.The largest pulse energy,minimum duration,and highest peak power obtained were 3.41?J,28.6 ns,and 110.0 W,respectively.These results represent the best record reached thus far in passive Q-switching with 2D saturable absorbers.